Theoretical Investigations of the Catalytic Role of Water in Propene Epoxidation on Gold Nanoclusters： A Hydroperoxyl- Mediated Pathway

We report a comprehensive theoretical investigation of the catalytic reaction mechanisms of propene epoxidation on gold nanoclusters using density functional theory （DFT）. We have shown that water acts as a catalytic promoter for propene epoxidation on gold catalysts. Even without reducible supports, hydroperoxyl （OOH） and hydroxyl （OH） radicals are readily formed on small-size gold clusters from co-adsorbed H20 and 02, with energy barriers as low as 4-6 kcal/mol （1 cal = 4.186 J）. Propene epoxidation occurs easily through reactions between C3H6 and the weakened O-O bond of the OOH radicals on the surfaces of gold clusters.

Hydrogenation of molecular oxygen to hydroperoxyl： An alternative pathway for O2 activation on nanogold catalysts

Activation of molecular O2 is the most critical step in gold-catalyzed oxidation reactions; however, the underlying mechanisms of this process remain under debate. In this study, we propose an alternative O2 activation pathway with the assistance of hydrogen-containing substrates using density functional theory. It is demonstrated that the co-adsorbed H-containing substrates （R-H） not only enhance the adsorption of O2, but also transfer a hydrogen atom to the adjacent O2, leading to O2 activation by its transformation to a hydroperoxyl （OOH） radical species. The activation barriers of the H-transfer from 16 selected R-H compounds （H2O, CH3OH, NH2CHCOOH, CH3CH=CH2, （CH3）2SiH2, etc.） to the co-adsorbed O2 are lower than 0.50 eV in most cases, indicating the feasibility of the activation of O2 via OOH under mild conditions. The formed OOH oxidant, with an increased O-O bond length of -1.45 A, either participates directly in oxidation reactions through the end-on oxygen atom, or dissociates into atomic oxygen and hydroxyl （OH） by crossing a fairly low energy barrier of 0.24 eV. Using CO oxidation as a probe, we have found that OOH has superior activity than activated O2 and atomic oxygen. This study reveals a new pathway for the activation of O2, and may provide insight into the oxidation catalysis of nanosized gold.

Hydroxyl,hydroperoxyl free radicals determination methods in atmosphere and troposphere

The hydroxyl radical(·OH)has a crucial function in the oxidation and removal of many atmospheric compounds that are harmful to health.Nevertheless,high reactivity,low atmospheric abundance,determination of hydroxyl,and hydroperoxyl radical’s quantity is very difficult.In the atmosphere and troposphere,hydroperoxyl radicals(HO_(2))are closely demanded in the chemical oxidation of the troposphere.But advances in technology have allowed researchers to improve the determination methods on the research of free radicals through some spectroscopic techniques.So far,several methods such as laser-induced fluorescence(LIF),high-performance liquid chromatography(HPLC),and chemical ionization mass spectroscopy have been identified and mostly used in determining the quantity of hydroxyl and hydroperoxyl radicals.In this systematic review,we have advised the use of scavenger as an advance for further researchers to circumvent some of these problems caused by free radicals.The primary goal of this review is to deepen our understanding of the functions of the most critical free radical(·OH,HO_(2))and also understand the currently used methods to quantify them in the atmosphere and troposphere.

衰荡光谱法测量OH自由基的理论研究

提出了一种用衰荡光谱法测量对流层OH自由基的新方法 ,并从理论上推导出OH自由基浓度与衰荡时间的关系 ,讨论了该方法的可行性和灵敏度 ,分析了各种干扰因素对测量的影响 ,认为该方法与传统测量OH自由基的方法相比优势较为明显。

电位控制辣根过氧化物酶在玻碳电极上的组装及H_2O_2的检测

研究了一种在聚硫堇修饰玻碳电极上利用电位控制组装辣根过氧化物酶（HRP）的新方法.首先将硫堇（TH）电聚合到玻碳电极（GCE）表面,形成均匀的带正电荷的导电聚合膜,再通过调节溶液的酸度使HRP带负电荷,利用电位控制的方法在硫堇聚合膜（PTH）上组装HRP,通过循环伏安法和电化学交流阻抗法对HRP的整个组装过程进行表征.在优化的实验条件下,采用计时电流法将HRP修饰电极用于H2O2检测,结果表明,在2×10^-5～2×10^-2mol·L^-1范围内HRP修饰电极的响应电流与H2O2浓度呈良好的线性关系,该研究对各类酶传感器、免疫传感器的设计与制备具有重要意义.

The degradation pathways of contaminants by reactive oxygen species generated in the Fenton/Fenton-like systems

Reactive oxygen species(ROSs)in Fenton process are of great importance in treating contaminants in wastewater.It is crucial to understand their chemical properties,formation,and reaction mechanisms with contaminants.This review summarizes the reactive oxygen species in Fenton process,including hydroxyl radical(·OH),superoxide radical(O_(2)·-),singlet oxygen(1O_(2)),hydroperoxyl radical(HO_(2)·),and high-valent iron.·OH shows a trend to react with chemistry groups with abundant electrons through H-atom abstraction,radical adduct formation and single electron transfer.Electron transfer is discovered to be an important pathway when1O_(2)degrades organic pollutants.Ring-opening andβ-scission are proposed to be the possible ways of1O_(2)to certain contaminants.Proton abstraction,nucleophilic substitution,and single electron transfer are proposed to explain how O_(2)·-degrade pollutants.As the conjugated acid of O_(2)·-,radical adduct formation and H-atom abstraction are reported for the reaction mechanisms of hydroperoxyl radical.High-valent iron in Fenton,namely Fe(IV),reacts with certain pollutants via single-or two-electron transfer.This review is important for researchers to understand the ROSs produced in Fenton and how they react with pollutants.

水在化学反应中的(助)催化作用研究进展

水广泛存在于众多化学反应体系中,除了提供反应媒介外,还发挥着很多其他的重要作用.近年来,水的(助)催化作用受到催化科学工作者的广泛关注,并且取得了一系列研究成果.本文从实验和理论两个方面,对水或水气在气相分子反应、液相反应及固体催化剂表面反应中的催化作用及机理进行了介绍和总结.

总状毛霉对20(S)-原人参二醇的微生物转化及条件优化

目的:利用微生物转化的方法构建20(S)-原人参二醇过氧衍生物的新合成途径,并对转化条件进行优化,提高过氧衍生物的产率。方法:选取总状毛霉Mucor racemosus AS 3.205为转化菌株,从接菌量,底物浓度,转化时间,加样时间,温度,转速等方面对转化条件进行优化。结果:获得2个20(S)-原人参二醇过氧衍生物,20(S)-原人参二醇为25,26-烯-24(R)过氧羟基-20(S)-原人参二醇和23,24-烯-25过氧羟基-20(S)-原人参二醇;获得了优化的转化工艺,即接种量为10%,底物浓度为0.25 mmol·L-1,加样时间为转种后48 h,培养温度为28℃,转化时间为5 d,摇床转速为150 r·min-1。结论:该方法能简便的获得20(S)-原人参二醇过氧衍生物,采用优化后的转化条件25,26-烯-24(R)过氧羟基-20(S)-原人参二醇和23,24-烯-25过氧羟基-20(S)-原人参二醇的产率均明显增大。

三七总皂苷酸水解产物化学成分研究

目的对三七总皂苷(PNS)酸水解产物化学成分进行研究。方法PNS用盐酸水解,水解产物采用各种柱色谱进行分离纯化,由波谱数据(HR-ESI-MS、ESI-MS、1H-NMR、13C-NMR、HSQC、HMBC)进行结构鉴定。结果从PNS酸水解产物中分离得到18个化合物,分别鉴定为达玛-25-烯-24-过氧羟基-3β,6α,12β,20S-四醇(1)、6α,12β,20S-三羟基-达玛烷-24-烯-3-O-β-D-吡喃葡萄糖基-(1→2)-β-D-吡喃葡萄糖苷(2)、6α,12β,20R-三羟基-达玛烷-24-烯-3-O-β-D-吡喃葡萄糖基-(1→2)-β-D-吡喃葡萄糖苷(3)、越南人参皂苷R8(4)、24(S)-拟人参皂苷GQ(5)、人参皂苷Rg5(6)、20(R)-人参皂苷Rg3(7)、20(R)-人参皂苷Rk2(8)、3β,12β-二羟基-达玛烷-E-20(22),24-二烯-6-O-β-D-木糖基-(1→2)-β-D-吡喃葡萄糖苷(9)、20(S)-人参皂苷Rg2(10)、人参皂苷SL1(11)、20(R)-人参皂苷Rh1(12)、20(22)E-人参皂苷Rh4(13)、25-羟基-20(R)-人参皂苷Rh1(14)、(3β,6α,12β,20S)-20,25-环氧-3-12-二羟基-达玛-6-O-β-D-吡喃葡萄糖苷(15)、20(R)-原人参二醇(16)、20(R)-原人参三醇(17)、20(S)-原人参三醇(18)。结论化合物1为1个新的四环三萜化合物,化合物2~5为三七及PNS转化产物中首次分离得到。

HO_(2)非均相摄取系数的测量与参数化

HO_(2)自由基与环境大气气溶胶的非均相反应是HO_(2)自由基的重要汇之一,对大气氧化能力有重要影响,对大气颗粒物的物化性质等进一步产生影响。HO_(2)的非均相反应过程的定量描述对不同地区大气氧化性与臭氧生成能力等问题的探求具有重要意义。目前不同研究小组测量的摄取系数可相差3到5个数量级,深入探究不同条件下不同种类气溶胶对HO_(2)自由基的非均相摄取机制,对摄取机制进行参数化表达,并准确测量摄取系数是量化其环境影响的关键。本文深入介绍了HO_(2)非均相摄取的原理与参数化表达,总结了已有的研究结果与进展,对不同的影响因素进行总结分析,并对此领域未来的发展方向提出建议与展望。